Many processes and devices have been used for color image processing and rely on a technique of creating look up tables (LUTs) to produce images on a passive or active display medium, such as paper or an electronic screen. In the printing of color images many customers use custom CMYK International color consortium (ICC) profiles as the source space for their documents. This allows them to emulate other presses on photocopier devices. The main problem with doing this is that during the CMYK to profile connection space (PCS) to CMYK translation, K only data is converted to CMYK. In addition, the customer is subject to a performance hit each time the ICC path is used. Prior to this invention, the customer would have to create a device link profile. Unfortunately, not all raster image processor (RIP) support device link profiles. Thus, a solution may not exist for some customers.
The generation of color documents can be thought of as a two step process: first, the generation of the image by means of scanning an original document with a color image input terminal or scanner or, alternatively, creating a color image on a work station operated in accordance with a color image creation program; and secondly, printing of that image with a color printer in accordance with the colors defined by the scanner or computer generated image.
Photo electronic scanning of a color image typically produces a separation of that image into red, green, and blue components which are output as RGB signals. In order to produce such an image in printed form, the RGB signal must be converted into a CMYK signal which can be read by suitable color printing apparatus. For scanning from a hard-copy original, the original calorimetric signals derived from the hard-copy image are typically in a red-green-blue (RGB) color space; however, most general purpose color printing apparatus , whether electrostatographic or otherwise, require that the calorimetric signal be applied to cyan-magenta-yellow (CMY) or cyan-magenta-yellow-black (CMYK) color space. Most full-color xerographic printers, for example, have supplies of cyan, magenta, yellow, and black toner, that are applied to different portions of an image to obtain subtle gradations of color in the visible spectrum.
An example of prior art of color image processing is disclosed in U.S. Pat. No. 5,787,193 by Balasubramanian entitled “System for converting color image signals from RGB to CMY color spaces through look-up tables” describes a system for converting RGB color signals to CMY or CMYK color signals, such as to operate a color printing apparatus, and utilizes three separate electronic look-up tables. Each look-up table allows inputs of RGB signals, which are applied to a three-dimensional space. Each point in the space represents an output for one CMY color signal, and each look-up table is dedicated to one CMY color output. Each look-up table emphasizes one particular RGB color by providing a higher resolution of inputs along the axis for that color. FIG. 1 illustrates a diagram of a prior-art system 100 for converting color image signals from RGB to CMY color spaces through look-up tables. FIG. 2 illustrates an example 200 of the locations of outputs in color space according to the prior-art system 100 shown in FIG. 1.
Another example of a prior art of color image processing is disclosed in U.S. Pat. No. 5,270,808 to Tanioka, which published on Dec. 14, 1993 and is entitled “Color image processing with adjustment of computed recording color to match original color”. It describes a color image processing method and apparatus therefore, in which the input image data are converted into a color coordinate system represented by luminosity and hue, for example L*a*b* space. The colors reproducible on the output device, for example a printer, are also converted into this coordinate system. An average value is calculated over plural pixels in the vicinity of an object pixel to be digitized, and plural average values are then obtained by including the object pixel selected at each of the reproducible colors. The input image signal is digitized to the closest one of the plural average signals. The digitization error generated upon digitization is distributed to the succeeding pixels with weighted ratios. This method achieves faithful color reproduction, matching the colors reproducible on the recording or display device. What are still needed are improved methods or systems for color translation.